Fabrication of semiconductor devices often involves many process steps. For example, the process of fabricating a field effect transistor usually includes doping a semiconductor substrate (e.g., adding desired impurities into the substrate) to form source/drain junctions. Many different methods may be implemented for doping the substrate, such as ion implantation, diffusion, and epitaxial growth. Further, the dopants introduced into the substrate often need to be electrically activated before semiconductor devices can be fabricated on the substrate. The activation of the dopants often includes dissolving dopant clusters, and transferring the dopant atoms/molecules from interstitial positions into lattice sites of the lattice structure of the substrate. As an example, the dopants may be activated using rapid thermal annealing (RTA), or millisecond thermal annealing (MSA).
Under certain circumstance, the fabrication process of semiconductor devices involves microwave radiation which typically includes electromagnetic waves with wavelengths ranging from 1 m to 1 mm (corresponding to frequencies between 0.3 and 300 GHz). When microwave radiation is applied to a certain material (e.g., a dielectric material) which includes electric dipoles, the dipoles change their orientations in response to the changing electric fields of the microwave radiation and thus the material may absorb the microwave radiation to generate heat. The response of the material to the electric field of the microwave radiation can be measured using a complex permittivity, ∈(ω)*, which depends on the frequency of the electric field:∈(ω)*=∈(ω)′−i∈(ω)″=∈0(∈r(ω)′−i∈r(ω)″)  (1)where ω represents the frequency of the electric field, ∈(ω)′ represents a real component of the complex permittivity (i.e., a dielectric constant), and ∈(ω)″ represents a dielectric loss factor. In addition, ∈0 represents the permittivity of a vacuum, ∈r(ω)′ represents the relative dielectric constant, and Σr(ω)″ represents the relative dielectric loss factor.
Whether a material can absorb the microwave radiation can be characterized using a loss tangent, tan δ:
                              tan          ⁢                                          ⁢          δ                =                                                            ɛ                ″                            ⁢                              μ                ′                                      -                                          ɛ                ′                            ⁢                              μ                ″                                                                                        ɛ                ′                            ⁢                              μ                ′                                      +                                          ɛ                ″                            ⁢                              μ                ″                                                                        (        2        )            where μ′ represents a real component of the magnetic permeability of the material, and μ″ represents a magnetic loss factor. Assuming negligible magnetic loss (i.e., μ″=0), the loss tangent of a material is expressed as follows:
                              tan          ⁢                                          ⁢          δ                =                                            ɛ              ″                                      ɛ              ′                                =                                    ɛ              r              ″                                                      ɛ                r                ′                            ⁢                                                                                                      (        3        )            
Materials with a low loss tangent (e.g., tan δ<0.01) allow microwaves to pass through with very little absorption. Materials with an extremely high loss tangent (e.g., tan δ>10) reflect microwaves with little absorption. Materials with an intermediate loss tangent (e.g., 10≧tan δ≧0.01) can absorb microwave radiation.